Anatomy of Pons

Anatomy of Pons

1. Pons anatomy Dr Vaishal Shah SR neurology GMC Kota

2. The pons is part of the metencephalon (pons and cerebellum)

3. Anterior surface

4. Posterior surface

5. Tracts pssing through pons The medial longitudinal fasciculus situated dorsomedially . PPRF – ventral to MLF. The medial lemniscus, lies dorsal to the corticospinal, corticobulbar, and corticopontine fiber bundles. The ventral spinocerebellar, spinothalamic. Lateral tectospinal, rubrospinal, corticopontocerebellar tracts. Auditory connections, including the lateral lemniscus, the trapezoid body, and the superior olivary nuclear complex. The brachium pontis or middle cerebellar peduncle connects the ventral pons with the cerebellum.

6. Blood supply of pons

7. Vascular supply Paramedian vessels - supply the medial basal pons, including the pontine nuclei, the corticospinal fibers , and the medial lemniscus. Short circumferential arteries - ventrolateral basis pontis .

8. Vascular supply Long circumferential arteries - most of the pontine tegmentum and part of the middle cerebellar peduncles Superior cerebellar artery - dorsolateral pons and brachium pontis , the dorsal reticular formation, and the periaqueductal region. Anterior inferior cerebellar artery – same area but in lower 2/3 pons Internal auditory artery - supplies the auditory, vestibular, and facial cranial nerves.

9. Symptoms in general Medial syndromes – Contralateral hemiparesis, ataxia Ipsilateral INO, conjugate horizonatal gaze palsy. Lateral syndromes – contralateral hemianaesthesia Ipsilateral ataxia, hornor’s syndrome, sometimes conjugate horizonatal gaze palsy Bradley’s neurology in clinical practice

10. Ventral pontine syndromes Millard- Gubler Syndrome – caudal ventromedial pons - basis pontis and the fascicles of cranial nerves VI and VII ( paramedian arteries ) Contralateral hemiplegia (sparing the face) is due to pyramidal tract involvement. Ipsilateral lateral rectus paresis (cranial nerve VI) with diplopia. Ipsilateral peripheral facial paresis (cranial nerve VII).

11. Ventral pontine syndromes Raymond Syndrome ( alternating abducens hemiplegia) – caudal ventromedial pons – ipsilateral abducens nerve fascicles and the corticospinal tract but spares cranial nerve VII (paramedian arteries) Ipsilateral lateral rectus paresis (cranial nerve VI) Contralateral hemiplegia, sparing the face, due to pyramidal tract involvement

12. Ventral pontine syndromes Pure Motor Hemiparesis – caudal ventromedial pons – corticospinal tracts in the basis pontis pure motor hemiplegia with or without facial involvement. Patient often have severe dysarthria and dysphagia. Bouts of uncontrollable laughter may also occur Other locations - posterior limb of the internal capsule, the cerebral peduncle, and the medullary pyramid

13. Ventral pontine syndromes Dysarthria—Clumsy Hand Syndrome – basis pontis at junction of upper 1/3 rd and lower 2/3 rd of pons facial weakness and severe dysarthria and dysphagia occur along with clumsiness, impaired finger dexterity, and paresis of the hand. Hyperreflexia and a Babinski’s sign may occur on the same side as the arm paresis, but sensation is spared. Other locations - lesions in the genu of the internal capsule or with small, deep cerebellar hemorrhages

14. Ventral pontine syndromes Ataxic Hemiparesis - basis pontis at junction of upper 1/3 rd and lower 2/3 rd of pons Hemiparesis that is more severe in the lower extremity. Hemiataxia on same side of paresis. Occasionally dysarthria, nystagmus, and paresthesias . The ataxia is unilateral, probably because transverse fibers originating from the contralateral pontine nuclei (and projecting to the contralateral cerebellum) are spared

15. Ventral pontine syndromes Ataxic Hemiparesis Other locations Contralateral thalamocapsular lesions Lesions of the contralateral posterior limb of the internal capsule Lesions of the contralateral red nucleus With superficial anterior cerebral artery territory infarcts in the paracentral area

16. Ventral pontine syndromes Locked-in Syndrome – Bilateral ventral pons ( infarction, tumour, haemorrhage, trauma, abscess, encephalitis, neuro- behcet’s , MS, CPM, heroin abuse, diazepam toxicity ) Quadriplegia due to bilateral corticospinal tract involvement in the basis pontis . Aphonia due to involvement of the corticobulbar fibers innervating the lower cranial nerve nuclei Occasional impairment of horizontal eye movements due to bilateral involvement of the fascicles of cranial nerve VI

17. Ventral pontine syndromes Locked-in Syndrome – Bilateral ventral pons Reticular formation is not injured, the patient is fully awake. Vertical eye movements and blinking are intact (the patient may actually convey his wishes in morse code)

18. Dorsal pontine syndromes Foville Syndrome - dorsal pontine tegmentum in the caudal third of the pons Contralateral hemiplegia (with facial sparing) due to interruption of the corticospinal tract. Ipsilateral peripheral-type facial palsy which is due to involvement of the nucleus and fascicle (or both) of cranial nerve VII. Ipsilateral conjugate gaze palsy (gaze is “away from” the lesion) due to involvement of the PPRF or abducens nucleus, or both.

19. Dorsal pontine syndromes Raymond- Cestan Syndrome - dorsal pontine tegmentum in rostral pons Ipsilateral Cerebellar signs (ataxia) with a coarse “ rubral ” tremor which is due to the involvement of the cerebellum Contralateral hypesthesia with reduction of all sensory modalities (face and extremities) which is due to the involvement of the medial lemniscus and the spinothalamic tract Ipsilateral Paralysis of conjugate gaze toward the side of the lesion (due to involvement of the PPRF).

20. LATERAL PONTINE SYNDROME Marie-Foix Syndrome - lateral pontine lesions affecting the brachium pontis Ipsilateral cerebellar ataxia - cerebellar connections Contralateral hemiparesis - corticospinal tract Variable contralateral hemihypesthesia for pain and temperature - spinothalamic tract

21. Rare presentations Anosognosia for the hemiplegia Blepharospasm Jaw-opening dystonia, hemidystonia , Dysarthria-dysmetria or dysarthria-facial paresis Body lateropulsion from paramedian tegmental involvement ventral to the fourth ventricle, Truncal ataxia without limb ataxia

22. Pontine haemorrhage Massive variety Classic picture of Coma Quardriplegia Horizontal ophthalmoplegia with/ withut ocular bobbing Pinpoint reactive pupil Abnormal respiratory pattern - “inspiratory gasps of apneustic respiration,” Cheyne–Stokes patterns, slow and labored respirations, and gasping and apnea Hyperthermia

23. Pontine haemorrhage 4 types Massive basal-tegmental bilateral tegmental Small unilateral tegmental

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